Raman-nath light diffraction by ultrasound in gyrotropic cubic crystals in an external electric field

Abstract

UDC 535.42:534.8 Investigation of light diffraction by ultrasonic (US) waves in gyrotropic cubic crystals in an external electric field is of scientific and practical interest [1 I, as a number of crystals with a structure of sillenite (Bi12GeO20, Bil2SiO20, Bil2TiO20, etc.) possess the high specific rotation of a light polarization plane and at the same time a substantial electrooptical effect. While in uniaxial and biaxial crystals the electric field-induced anisotropy is manifested only for light propagations close to the optical axes, in a cubic crystal the anisotropy must be taken into account for any geometry of acoustooptical (AO) interaction [2 ]. It is interesting to investigate the simultaneous influence of gyrotropy and electroinduced anisotropy on AO diffraction in cubic crystals. The AO Raman-Nath diffraction in gyrotropic crystals has been considered in an approximation of a given polarization [3, 4 I. For calculation of the complex vector amplitudes of diffracted waves, they were decomposed into circularly polarized components. In [5 ], a system of equations of coupled waves is given that describes specific features of the Raman-Nath AO diffraction in gyrotropic cubic crystals with the strong light-ultrasound interaction without allowance for the influence of electroinduced anisotropy of the crystal in an external electric field. In [6, 7 ], consideration is given of the influence of an external electric field on the Bragg light diffraction by ultrasound in gyrotropic crystals. It is shown that the combined influence of gyrotropy and acousto- and electroinduced anisotropy causes a substantial change in the polarization and energy characteristics of diffracted waves. Some peculiar features of the Bragg AO diffraction by confined light beams in gyrotropic cubic crystals are discussed in [8 ]. A promising use of biaxial gyrotropic crystals for creation of AO filters is shown in [9 I. In the present work we investigate the Raman-Nath AO diffraction in gyrotropic cubic crystals in an external electric field by solving numerically a system of reduced equations obtained by the method of slowly changing amplitudes. From the Maxwell and material equations 12, 10 ] of a gyrotropic crystal in an external electric field a wave